Control system for grinding machines



Aug. 18, 1910 e;- D. Ru 3,524,285

CONTROL SYSTEM FOR GRI ND ING MACHINES Filed Aug. 9, 1966 V 3 Sheets-Sheet 1 I4 ggsgfig HYDRAULIC SERVO SERVO CIRCUIT VALVE L Ema" 2o-- 2 INVENTOR.

RICHARD D. RUTT Aug. 18, 1970 R. D. RUTT ,5 ,2

CONTROL SYSIIEMFOR GRINDING MACHINES Filed Aug. 9, 1966 5 Sheets-Sheet 2 SERVO VALVE CONTROL G RIND CONTROL SIGN AL FIG. 3.

RICHARD D. RU TT "kZJM Aug; 18, 1970 ,R. D. RUTT CONTROL SYSTEM FOR GRINDING MACHINES Filed Aug. 9, 1966 3 Sheet$-$heet 5 w VARIABLE SPEED GENERATOR I TRANSMISSION SERVO I I! A VALVE 24 I84 I85 TR -80 SELF 3 SYNCHRONOUS I MOTOR /l82 FIG. 5.

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/2OO L94 98 w T I00 INVENTOR. RICHARD D. 'RUTT United States Patent 3,524,285 CONTROL SYSTEM FOR GRINDING MACHINES Richard D. Rutt, Wilson, N.Y., assignor to The Carborundum Company, Niagara Falls, N.Y., a corporation of Delaware Filed Aug. 9, 1966, Ser. No. 571,271 Int. Cl. B24b 21/04, 21/12 US. Cl. 51-135 Claims ABSTRACT OF THE DISCLOSURE A system for controlling and adjusting the grinding pressure of an abrasive belt in accordance with the wear conditions of the belt so as to achieve a constant stock removal rate and extended belt life incorporates a variable speed drive interposed between an infeed roll and a time schedule controller. The latter operates a linear motion resistor operatively connected to means for increasing the grinding pressure on the belt.

This invention relates to control systems for grinding machines and, more particularly, to a novel method and apparatus for controlling the pressure between an abrasive surface and stock material.

In the art of metal conditioning, it is customary to remove a thin layer of metal from the surface of a continuous strip of stock metal because of the inferior mechanical properties of such surface caused by inclusions and other defects. This undesirable layer is removed at a grinding station by means of a coated abrasive belt as the work advances thereby at a uniform speed.

A major consideration in conditioning strip stock is to remove only that amount of surface material which will eliminate the imperfections therein. Many conventional grinders operate on the principle of a fixed grinding orifice which sizes the material to a predetermined uniform thickness. Since strip stock is seldom uniform in thickness throughout its length, more material than is necessary is removed resulting in a drastic reduction of yield per coil of material. Some attempts have been made to overcome this problem by employing a machine having a floating grinding head which rides on the stock at constant pressure and follows the contour of the strip. However, this type of grinding machine does not compensate for belt wear and accordingly does not obtain the greatest possible yield from each coil of material.

One of the critical problems confronted in the utilization of abrasive belts is that the belt will remove material at a much faster rate when new than it will when it becomes somewhat worn. The grind pressure is usually greater than necessary at the early stages of the belts useful life and results in a very severe shedding of grain so as to quickly render the belt worn and dull. If insufiicient grind pressure is applied to the belt as it becomes worn, the belt merely slides across the workpiece without removing the proper amount of stock. Accordingly, the minimum grinding pressure necessary to do the work is preferable when the belt is new and, as the belt becomes worn and dull with use, it is desirable to increase the grinding pressure sufficiently to continue doing a satisfactory job.

An operator may be employed to incrementally adjust the grind pressure from modest values at the beginning of the use of the belt to increasing pressures during its life and thereby extend the useful life of the belt. Not only does this procedure require the constant attention of the operator, but it is obvious that efficiency is sacrificed since the stepped increase of pressure would not always be the optimum amount for the continuously wearing belt.

Patented Aug. 18, 1970 The apparatus of the present invention, as hereinafter described, provides a solution to the above problem by incorporating novel means in a control system for constantly adjusting in infinite steps the grind pressure on an abrasive belt as the belt wears. This novel means obtains the greatest possible yield from each coil of strip mate rial and is particularly important in conditioning todays costly exotic metals.

Accordingly, it is an object of the present invention to provide a new and improved grinding machine.

It is another object of the present invention to provide a new and improved control means in a grinding machine for controlling the pressure applied to an abrasive belt.

It is still another object of the present invention to provide a new and improved control means in a grinding machine for removing a constant minimum amount of material, as dictated by the surface condition of the material, regardless of the varying thickness of such material.

It is a further object of the present invention to provide a new and improved control means in a grinding machine for adjusting the pressure applied to an abrasive belt in accordance with wear of the belt.

These and other objects of the present invention will become more apparent upon consideration of the following detailed description thereof when taken in conjunction with the following drawings, in which:

FIG. 1 is a schematic side elevational view of a grinding line incorporating the grinding apparatus of this invention;

FIG. 2 is an electrical diagram of the power responsive servo control circuit;

FIG. 3 is a diagrammatic view illustrating the hydraulic circuit for the backup roller;

FIG. 4 is a schematic view of the servo valve;

FIG. 5 is a diagrammatic view of the program control unit which is incorporated in the circuit diagram of FIG. 2; and

FIG. 6 is a view illustrating the mechanism of the program control unit.

Referring to the drawings and particularly to FIG. 1, it will be observed that a preferred embodiment of the grinding machine constructed in accordance with the principles of this invention comprises a grinding head, generally designated 10, enclosing an electric motor 12 having a power shaft 14 to which is rigidly secured a drive pulley 16. An endless abrasive belt 18 extends between drive pulley 16 and an idler pulley 20 rotatably mounted within the grinding head 10. If desired, the

drive and idler pulleys may be reversed so that the drive pulley is disposed adjacent the workpiece W.

The workpiece W is in the form of a continuous strip of stock which is advanced in the direction of the arrow from a payoff roll 22 through a tensioning means (not shown), over an infeed roll 24, beneath a guide roll 26, through the grinding head 10, under a guide roll 28, over an outfeed roll 30 and ultimately to a take-up roll 32.

A backup roller 34, commonly referred to as a grind pressure or billy roll in the art, is mounted in the grinding machine opposite the idler pulley 20 and is adapted to engage the workpiece on the surface opposite the surface being ground and polished. The backup roller 34 urges the workpiece W against the abrasive belt 18 and the depth of metal removed from the surface of the workpiece depends primarily upon the force imposed by the roller 34. A hydraulic control system positions the backup roller 34 relative to the abrasive surface in response to an electrical signal which varies as a function of the grinding head motor as will hereinafter be more fully explained. if

As shown schematically in FIG. 1, the backup roller 34 is rotatably mounted on a piston rod 36 secured to a piston 38 which is contained within a hydraulic cylinder 40. Hydraulic fluid is supplied to cylinder 48 through a pair of conduits 42 and 44 and fluid flow in these conduits is controlled by a hydraulic servo control valve 46, which in turn is controlled by a power responsive servo control circuit 48 having a control signal therein responsive to the current in the abrasive belt motor 12. Current in the motor 12 increases as the grinding pressure increases and therefore the grinding pressure can be regulated as a function of the power consumption of motor 12.

The power responsive control circuit is shown diagrammatically in FIG. 2. The primary winding 50 of a current transformer 52 is connected in series circuit with one of the three phase current conductors carrying the load current to the grinding motor 12. Consequently, a potential appearing across the secondary winding 54 of the current transformer 52 is proportional to the current drawn by the motor. Another transformer 56 has its primary Winding 58 connected across two of the three phase connections to the grinding motor 12 to develop a potential across its secondary winding 60 that is propertional to the potential supplied to the motor. The potential produced by the secondary winding 54 is dropped across an adjustable resistor 62, which adjusts the voltage that is created by the current transformer 52. The potential developed across the secondary winding 60 is dropped across a reactor 64 which is provided with an adjustable tap to permit adjustment of the reference level of the signal. When properly adjusted, the reactor 64 causes the system to respond only to changes in grinding pressure. Thus, the power consumed in driving the abrasive belt pulley and associated contact rolls, tracking pulleys and abrasive belt while idling are not measured by the system.

The reactor 64 supplies a certain proportion of the potential dropped across said reactor to an inductor 66. Inductor 66 receives a certain proportion of the potential output of the transformers 52 and 56 and mixes these potentials to develop a combined EMF across the inductor 66 representing in-phase components from the transformers 52 and 56. Consequently, the potential dropped across the inductor 66 reflects the power consumption from the grinding motor 12. Currents set up by this potential are rectified through a full-wave rectifier 68, the output thereof being smoothed by a filter network comprising capacitors 70 and 72 and a resistor 74 linking them. As a result, a well-filtered direct current flows in the conductor 76 which is proportional to the power or Servo valve control unit 80 includes another winding 82 which is supplied with a reference current derived from another source. For this purpose, an additional transformer 84 has its primary winding 86 connected to a source of alternating current potential. The output potential developed across a secondary winding 88 of transformer 84 is rectified through a full-wave rectifier 90 and filtered through filter capacitors 92 and 94 and through an inter-connecting filter resistor 96. The resulting DC signal produced by this filter network develops a constant potential across Zener diode 98. The constant potential thus produced develops a current through a variable resistor or potentiometer 100 and through the control winding 82 of the servo valve control unit 80. Zener diode 98 assures that the maximum voltage does not exceed the voltage rating of the control winding 82 and also acts as a voltage regulator to hold constant any current setting for the control winding 82 as determined by the resistance of the potentiometer 100. The two currents set up in the windings 78 and 82 of the servo valve control unit 80 operate to balance the condition of the valve 46 in accordance with the sum of the control influence exerted by the currents in both windings. Incorporated in the circuitry of FIG. 2 is a program control unit 180 located between potentiometer 108 and control winding 82, the purpose of which will be hereinafter explained.

In an electrically operated continuously variable servo valve such as will hereinafter be more fully described, there is the possibility that certain conditions such as friction or viscosity, for example, might impede small displacements of the valve in response to the control exerted upon the mechanism. To insure that the signals set up in the control windings 78 and 82 result in bringing the servo valve to the correct control condition, a small AC signal is introduced into the conductor 76 through a coupling transformer 102, which receives its input potential from a tapped reactor 104 connected across the secondary winding 88 of the reference potential transformer 84. The resulting AC ripple, called a dither signal, by its influence upon the control winding 78 of the servo valve, introduces a vibration into the operation of the valve which overcomes the effects of friction and viscosity.

Referring now to the diagrammatic showing of the hydraulic circuit in FIG. 3, it will be seen that a source of hydraulic fluid is contained within a suitable tank or reservoir 130. Hydraulic fluid in the system is drawn from the reservoir through a filter 132 by a constant flow pump 134 which is driven by a constantly energized electric motor 136. Pump 134 delivers fluid under pressure through a conduit 138 to an adjustable relief valve 140, which determines the pressure available in the system and applied to the servo valve. A return conduit 142 leads from the valve 148 to a check valve 144 and returns the fluid to the reservoir 130. Also leading from the relief valve is a pressure conduit 146 which is connected to the servo valve 46. A return line 148 connects the servo valve 46 to the return conduit 142.

As shown schematically in FIG. 4, the servo valve control unit 80 includes the control windings 78 and 82 which form a torque motor acting on an armature 150 pivotally mounted on a fulcrum 152. Mounted on one end of the armature 150 and positioned thereby is a spool valve 154 located in servo valve 46 and having a pair of enlarged portions or annular projections 156 and 158. A bore 160 is provided in the servo valve housing for slideably containing the spool valve 154, A passageway 162 is formed in the servo valve housing and communicates with the upper side of piston 38 by way of conduit 42. A second passageway 166 is formed in the housing and communicates with the underside of the piston 38 by means of the conduit 44. Pressure conduit 146 is connected to the bore 160 of servo valve 148 by means of a passageway 170. A pair of passageways 172 and 174 connect the bore 160 to the return line 148 which leads to tank 130.

The Zener controlled bias power provided supplies current to control winding 82 and the magnitude of this current is adjustable by means of the potentiometer 100 to obtain the desired grinding pressure. This grinding pressure depends to some extent on the grit size of the abrasive belt, the composition of the abrasive grain, the amount of stock to be removed and the material of which the workpiece is formed. A current is supplied to control winding 78 which is proportional to the current drawn by the grinding motor 12 when pressure is applied to the abrasive belt 18.

When the magnetic fields around control windings 78 and 82 are balanced, the armature 150 will be in its neutral position as illustrated in FIG. 4 and the annular projections 156 and 158 of spool valve 154 will obstruct any flow of fluid to the cylinder 40. In the neutral position of the spool valve 154, fluid under pressure in cylinder 40 maintains the backup roller 34 in engagement with the workpiece for urging the same against the abrasive belt with the desired constant grinding pressure.

In operation, the grinding head 10 removes a layer of material of constant thickness from the upper surface of the workpiece as it advances through the grinding head. Whenever a transverse ridge projecting from the upper surface of the workpiece engages the abrasive belt, the grinding pressure increases causing a greater load on motor 12 which in turn is reflected in control Winding 78. Since the value of the magnetic field about control winding 78 will then be greater than the preset reference value of control winding 82, armature 150 pivots in a clockwise direction displacing the spool valve 154 to the left to establish communication between the pressure conduit 146 and conduit 42 leading to the upper side of piston 38.

Thus, fluid under pressure is directed to the upper sideof piston 38 to urge the same downwardly until the grinding pressure is reduced to equal the preset value. Fluid from the lower side of piston 38 is displaced through conduit 44, passageway 166, passageway 174, conduits 148 and 142 to tank 130.

Conversely, if the current in winding 78 should become less than the current in winding 82 due to the presence of a depression in the workpiece W, armature 150 swings in a counterclockwise direction to establish communication between the pressure conduit 146 and conduit 44. This increases the pressure on the lower side of piston 38 to urge the same upwardly until the grinding pressure is increased to and equals the preset value. Thus, the grinding pressure remains substantially constant and the abrasive belt 18 will automatically remove a surface layer from the workpiece W of a predetermined depth although the thickness of the workpiece may vary. The position of the backup roller 34 changes in response to the hydraulic pressure in the cylinder 40 as a result of displacement of the spool valve 154 as controlled by the servo valve control unit 80, which in turn responds to the power responsive servo control circuit 48. Any tendency of the grinding motor power consumption to increase or decrease results in automatic correction in the grinding apparatus by an amount suflicient to maintain the power drawn by the grinding motor at a constant level. The system of this invention, therefore, adjusts automatically to variations in thickness of a workpiece as it passes under the grinding head.

As hereinbefore mentioned, a coated abrasive belt will remove stock at a faster rate when it is first applied to a workpiece than it will afterward. An important feature of the present invention is the provision of means for adjusting or modifying the grind pressure setting of potentiometer 100 in order to compensate for abrasive belt wear. The means for accomplishing this result are illustrated diagrammatically in FIG. as a program control unit 180 which operates a variable resistor, generally designated 182, incorporated in the electric circuitry of FIG. 2 between control winding 82 and potentiometer 100.

As shown in the diagrammatic illustration of FIG. 5, the infeed roller 24 is operatively connected to a variable speed transmission 184, which in turn is operatively connected to a self-synchronous generator 185. Generator 185 drives a self-synchronous motor 186, which drives a cam 188 (FIG. 6) suitably rigidly secured to a rotatable shaft 189 and contained within the housing 187 of the program control unit 180. Inasmuch as self-synchronous motor mechanisms are well-known, a detailed illustration or description thereof is believed unnecessary.

The structure of the program control unit 180 is shown in FIG. 6 and comprises a cam follower 190 provided with a roller 192 at the free end thereof which is biased into engagement with the periphery of the cam 188. Cam follower 190 is suitably rigidly mounted on a rotatable shaft 194 onto which is also rigidly mounted a wiper arm or slidable contact member 196 engageable with a slide wire 198 of the variable resistor 182. As shown in FIG. 2, the other end of contact member 196 is electrically connected to a conductor 200 leading from the potentiometer 100. As the cam rotates in the direction of the arrow as shown in FIG. 6, pivotal movement is imparted to the cam follower 190 and thereby the slide wire contact member 196 for elfecting a decrease in the resistance of resistor 182. Cam 188 is designed to make one revolution per life of a coated abrasive belt.

In operation, the advancing workpiece causes rotation of infeed roller 24 which in turn eifects rotation of cam 188 through means of the variable speed transmission 184, self-synchronous generator and self-synchronous motor 186. With reference to FIG. 6, which illustrates the starting position of cam 188, it will be seen that as the cam rotates counterclockwise, the cam follower 190 moves at a relatively faster rate at the beginning of cam rotation than it does subsequently. The resistance of variable resistor 182 is accordingly affected to establish a low preset grinding pressure at first, which is rapidly increased at the outset and then increased at gradually decreasing intervals for the life of the belt. Thus, as stock is removed and the belt continues to wear, the cam effects an increase in grinding pressure in exact accordance with the needs for constant stock removal and maximum belt life.

Although only one grinding head has been shown and described for illustrative purposes, it should be appreciated that two or more grinding heads may be employed in the grinding line, as desired. It is also obvious that the grinding head need not be oriented'as illustrated in FIG. 1 but may be disposed, for example, oriented 180 from the illustrated position.

As a result of the present invention, an improved grinding apparatus of the type incorporating a coated abrasive belt is provided for grinding strip stock in an improved and more efficient manner. By the provision of a program control unit, the preset grinding pressure may be automatically adjusted to compensate for belt wear in order to provide for accurate constant stock removal and extended useful belt life.

A preferred embodiment of the prinicples of this invention having been hereinbefore described and illustrated, it is to be realized that modifications thereof can be made without departing from the broad spirit and scope of this invention as defined in the appended claims.

I claim:

1. In a control system for grinding machines having an abrasive element and an infeed roller engageable with and rotated by a workpiece as it advances thereby comprising: an electric motor for driving said abrasive element; means for generating a signal responsive to current drawn by said motor; means for generating a reference signal; means for continually modifying said reference signal to compensate for continuous wear of said abrasive element; means for comparing said signals; and means responsive to said comparing means for adjusting the grinding pressure of said abrasive element on the workpiece.

2. A control system as defined in claim 1 wherein said means for continually modifying said reference signal comprises a variable resistor having a slidewire and a movable contact member engagable therewith.

3. A control system as defined in claim 2 wherein said means for continually modifying said reference signal includes means for effecting movement of said movable contact member.

4. A control system as defined in claim 3 including means repsonsive to the speed of rotation of said infeed roller for actauting said means for effecting movement of said movable contact member.

5. A control system as defined in claim 4 wherein said means for effecting movement of said movable contact comprises a program control unit having a housing, a rotatable cam located in said housing, a shaft rotatably carried by said housing, a cam follower mounted on said shaft and engagable with said cam, said contact member being rigidly mounted on said shaft and rotatable therewith.

6. In a control system for grinding machines having an abrasive element, an electric motor for driving said abrasive element, an infeed roller engagable with and rotated by a workpiece as it advances thereby, and a backup roller engagablc with the workpiece opposite said abrasive element comprising: means for generating a signal responsive to current drawn by said motor, said current reflecting the grinding presusre applied to the workpiece; means for generating a reference signal; means for continually modifying said reference signal to compensate for continuous wear of said abrasive element; means for comparing said signals; means for adjusting the spacing between said backup roller and said abrasive element; and means responsive to said comparing means for actuating said adjusting means to vary the space between the abrasive element and backup roller to maintain constant stock removal.

7. A control system as defined in claim 6 wherein said means for continually modifying said reference signal comprises a variable resistor having a slidewire and a movable contact member engageable therewith.

8. A control system as defined in claim 7 wherein said means for continually modifying said reference signal includes means for effecting movement of said movable contact member.

9. A control system as defined in claim 8 including means responsive to the speed of rotation of said infeed roller for actuating said means for effecting movement of said movable contact member.

10. A control system as defined in claim 9 wherein said means for effecting movement of said movable contact comprises a program control unit having a housing, a rotatable cam located in said housing, a shaft rotatably carried by said housing, a cam follower mounted on said shaft and engageable with said cam, said contact member being rigidly mounted on said shaft and rotatable therewith.

References Cited UNITED STATES PATENTS 2,168,596 8/1939 Hall 51-111 2,333,978 11/1948 Bowman 51--137 X 2,648,176 8/1953 Zimmerman 51-135 3,271,909 9/1966 Rutt et a1. 51138 X 3,394,501 7/1968 Carlson et al. 51-138 3,415,017 12/1968 Murray 51-135 HAROLD D. WHITEHEAD, Primary Examiner US. Cl. X.R. 51-139, 165 

